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| Titel |
Elemental (C/N ratios) and Isotope (δ13CTOC, δ15NTN) Compositions of Surface Sediments from the Barrier Islands in the Nakdong River Estuary, South Korea |
| VerfasserIn |
Jun-Ho Lee, Han Jun Woo, Kap-Sik Jeong, Jeongwon Kang, Jae Ung Choi, Dong-Hun Lee |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250147354
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| Publikation (Nr.) |
 EGU/EGU2017-11507.pdf |
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| Zusammenfassung |
| The Nakdong River Estuary (NRE) in South Korea is a typical, artificially-manipulated
estuary and blocked by two large dam. The Noksan Dam, built in 1934, blocks the flow of the
West Nakdong River, and the NRE Dam was completed between 1983 and 1987 to regulate
the flow of the East Nakdong River (called the Eulsuk River locally). For the past half
century, several huge industrial complexes have been developed in the reclaimed land near
the NRE. In the estuary, the hydraulic circulation has been markedly modified caused by the
changes in the river discharge and geomorphic configuration of such as the formation of a
series of barrier islands, the two large dams resulting from the artificial control of the natural
river flow and upstream intrusion of saltwater by the operation of the two large dams.
Consequently, the saltwater wedge that once reached approximately 40 km upstream is now
blocked at the dam, considerably reducing the tidal prism. The estuary is typified by
barrier-lagoon system with various subenvironments and microtidal with a 1.5 m tidal
range.
We investigated the elemental (C/N ratios) and isotopic (δ13CTOC, δ15NTN)
compositions of organic matters in various composition in the surface sediments in the NRE.
In May 2015, 90 surface sediment samples were collected on and around three islands in the
NRE. The mean grain size of the barrier island system in the NRE ranged from 1.1 to 8.9 Φ
(average 3.9 Φ) in mean grain size, and they were composed of various sediment types,
including muddy Sand (S), sandy Mud (sM), and Mud (M). A useful application of the C/N
ratios is as a proxy for assessment of organic matter source change, related to the sediment
origins terrestrial or marine. The C/N ratios (average, 5.88) imply that the organic
matter in the study area was of marine origins, as indicated by the lower ratios
between 4 and 10. The isotope composition of sedimentary organic matter (δ13CTOC,
δ15NTN) indicated the deposition of algae-derived organic matter with limited input of
terrestrial organic matter. The carbon isotopic values (δ13CTOC) ranged from –28.2
to –16.8 permil VPDB (average, –22.5 permil VPDB), with a nitrogen isotopic
values (δ15NTN) in the range of 6.2–12.5 permil AIR (average, 9.4 permil AIR) and
C/N ratios in the range of 4.6–7.3 (average, 11.3). These results suggest that the
microphytobenthos contribution was greater than the inflow of surrounding land
vegetation and had a general marine origin to the north from the barrier islands in the
NRE. To the south, the effect was considered mixed. The elemental and isotope
compositions of surface sediments in the NRE can contribute to understanding
of the biochemical behavior of organic matter around the barrier island system
associated with environmental changes caused by coastal construction. Further
studies should determine the effects of end-member discrimination on the origins of
the organic matter such as advance signature proxy. It is necessary to continue
measurements of sediments and water in the brackish water zone around the barrier system
from the tidal current vectors at these locations with on-site monitoring results. |
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